The structure parameter "degree of unsaturation," which is defined for a structural unit composed of hundred carbon atoms, is proposed for the assessment of characteristics of high-molecular-mass organic compounds. The introduction of the structure parameter has been substantiated. For the natural bitumen and fractions of its hydrogenation products used as an example, it has been shown that the density is linearly related to the number of bonds and the average molecular mass correlates with the parameter of unsaturation in the structural unit. The proposed structure parameter can be used for tentative classification of high-molecular-mass hydrocarbons and their processing products.